Conventional fossil fuels are gradually becoming depleted. Among the available sustainable energy sources, solar energy is undoubtedly one of the cleanest, most common and most promising alternative energy sources. Solar power generating devices, also known as solar cells or photovoltaic cells, are able to convert solar energy directly into electrical energy. Their power generation mechanism is based on the photovoltaic effect of semiconductor PN junction.
With the development of science and technology, a new type of solar cell, the passivated emitter rear contact (PERC) solar cell, has appeared. It is a type of newly developed, highly efficient solar cell that has attracted widespread attention from the industry. Its core technology is as follows: the back surface of a silicon wafer is covered with a thin film of alumina or silica (5 to 100 nm) to gain the functions of passivating the surface and improving long-wave response, so as to increase the conversion efficiency of the solar cell. However, since alumina and silica are not electrically conductive, openings need to be made at certain locations on the film in order to enable contact between the metal aluminum and silicon wafer surface to capture electric current. On the other hand, during the process of high temperature sintering, metal aluminum (typically aluminum paste) may compromise the passivation effect of alumina or silica. As a result, a silicon nitride film is used to further cover the top of the alumina or silica film in order to provide a protective function.
The process currently available for producing passivated emitter rear contact solar cells comprises the following major steps: removing the damaged layer on the surface of the silicon wafer, texturing, diffusion, back polishing, etching, removing the glass impurity, back surface depositing of alumina or silica film, depositing of con nitride protection film, front surface depositing of silicon nitride antireflective layer, making local openings on the back surface, screen printing of metal paste on both the front surface and the back surface, and sintering, so as to prepare a solar cell.
However, the preparation process described above has a few problems: (1) it has many steps in the preparing process, which leads to a relatively high production cost, and accordingly, it must be improved in order to reduce production cost; and (2) the photoelectric conversion efficiency obtained from such prepared passivated emitter rear contact solar cells is still relatively low, and thus there is room for further improvement.